Series type time delay relay



April 7, 1970 l g H. G. suer-:RG

SERIES TYP TIME DELAY RELAYl Filed April 29, 1966 INVENTOR ATTORNEYS United States Patent O 3,505,642 SERIES TYPE TIME DELAY RELAY Hemming G. Siiberg, Union, NJ., assignor to Wagner Electric Corporation, a corporation of Delaware Filed Apr. 29, 1966, Ser. No. 546,229 Int. 'CL H0111 61/02 U.S. Cl. 340-52 10 Claims ABSTRACT OF THE DISCLOSURE A time delay relay of the type having a buckling member moveable between a rst and second circuit control-y ling position by expansion and contraction of an electrically conductifve expansible pull means is provided in 'which a resistor having a positive temperature coefficient of resistance is provided for controlling the expansion of the pull means. The resistor is connected in parallel with and to the midpoint of the pull means to control the current flowing in the pull means to prevent expansion of the pull means and consequent movement of the buckling member from one circuit controlling position to another when the relay is energized. A heater is also provided adjacent the resistor to increase its resistance and conjointly increase current ow in the pull means until the pull means expands suiciently to move the buckling member to the other circuit controlling position to energize an external load.

The present invention relates to a series type snap action relay having means for providing extended time delays.

In most time delay devices now in use, a heat sensitive bimetallic strip is usually incorporated as an element of the device to prevent premature operation thereof. This heat responsive strip, when cold, will maintain a pair of contacts in a normally closed position. Heating of the bimetallic strip either directly or indirectly causes its metals to expand differentially and causes movement of a portion thereof in a direction to open the contacts.

Bimetallic devices are relatively slow in responding tor heat and therefore they provide a time delay between application of the voltage to the terminals and opening of the circuit. The duration of the time delay is directly related to the coeflicient of expansion of the metals which comprise the strip and also to the mass thereof. Although devices of this type have proved useful in certain applications, they are expensive to produce and are limited in the length of the time delay which they can provide. Furthermore, they must be designed to handle the specific voltage of the circuit wherein they are employed. To eliminate these disadvantages, the series type time delay relay of the present invention was devised.

In comparison to the bimetallic units mentioned above, series type snap action devices such as circuit breakers, ilashers and hot wire switches are relatively `fast acting. Known flashers of this type comprise a buckling member which is deformed along one axis and held by an expansible pull means in a constrained position against the bias of deformation. When current is passed through the device and the load, the pull means expands and permits the buckling member to snap toward its bias position. This opens the load circuit and permits the pull' means to cool and contract thereby snapping the buckling member back to the circuit closing position. Such a flasher is described and claimed in Schmidinger Patent No. Re. 24,023.

In accordance with the present invention, a series type snap action device is modied so as to function as a relay and also to provide an extended time delay prior to operation. The invention consists in connecting the ice pull means of the series device in parallel with a resistive means having a high positive temperature coe1licient of resistance. A heater positioned adjacent to the resistive means will heat that means and increase its resistance. When voltage is first applied across the terminals of the relay, the current will be insufficient to expand the pull ribbon, due to the parallel path through the resistive means. As the temperature of the resistive means increases under the influence of the heater, a greater proportion of current flows through the pull means causing it finally to expand and snap the buckling member. With the buckling member snapped, a load circuit or the like is closed and the heater circuit is opened. A delay in closing the load circuit is thus achieved. Subsequent to this operation, a suicient current will continue to ilow into the pull means to maintain the buckling member in snapped position. In one embodiment of this invention, the pull means current is maintained because of a fixed connection to the center thereof, which connection is connected to one side of the source. The pull means thus remains in its expanded state until the original voltage is removed.

In another embodiment of the invention, a normally closed contact on the center of the pull means replaces the fixed connection. Heat is maintained in the pull means by a separate heater which is provided in proximity to the pull ribbon or wrapped around it and the circuit of which is closed in the snapped position of the buckling member. This insures that the pull ribbon will remain in its expanded state until the voltage is removed.

For a better understanding of the invention and of specific embodiments thereof, reference may be had to the accompanying drawings of which:

FIG. 1 is a diagrammatic representation of a series type time delay relay embodying the invention and having a lead wire fixed to the center of the pull means.

FIG. 2 is a similar diagram showing another embodiment vof the new relay in which separate heating means are provided in proximity to the pull means and the lead wire is connected to the pull means by a normally closed contact.

IIG. 3 is a circuit diagram of the relay of FIG. 1; an

FIG. 4 is a circuit diagram of the relay of FIG. 2.

The relay of FIG. 1 includes a base 2 of insulating material through which extend three terminals 4, 6 and 8 for connection to an external circuit. A support post 12 is secured to the base 2 and the far side of a buckling member 10 as viewed in FIG. l is mounted on the upper end of the support 12. The support 12 is preferably an extension of the terminal l6 which can be connected to the positive side of the source. The buckling member 10 is bent or deformed about the longitudinal axis indicated at 14 so as to be normally convex toward the viewer. A pull means 16 overlies the normally convex side of member 10 and is secured under tension at its Mends to diagonally opposite corners of the buckling member 10, these corners being turned toward the opposite surface of the buckling member to provide anchorage for the pull means.

A contact 20 is positioned on the buckling member 10 adjacent the lower right corner, as viewed in FIG. 1 and a fixed contact 21 is suitably supported from base 2 and positioned for engagement with contact 20 when the pull means is cold. One end of a coil 22 is electrically connected to contact 21 and the other end of the coil is connected through a bleeding resistor 24 to a post 26 which comprises a continuation of terminal 8. Coil 22 is of material having a high positive temperature coefficient of resistance. Terminal 8 can be connected to the negative side of the source. The junction of the coil 22 and resistor 24 is permanently lixed at 28 to the pull means 16 substantially at its mid-point, A heater winding 30 is positioned Within the coil 22 with one end of the wind ing connected to a fixed contact 18. Contact 18 is suitably supported from the base 2 and normally engages a contact 19 which is positioned on the buckling member adjacent its lower left side as viewed in FIG. 1. The other end of the heater winding 30 is connected to the negative side of the source through post 26 and terminal 8. The coil 22 and heater winding 30 can be supported by an insulated mandrel (not shown) extending vertically from the relay base 2. A contact 32 is mounted on a mandrel 34 and is held away from a contact 31 which is positioned on the normally concave side of the buckling member 10. Current flows through contacts 31 and 32 only when the buckling member assumes its biased position due to expansion of pull means 16. Mandrel 34 is joined to the terminal 4 which may be connected to an external load 36 as shown in FIG. 3 of the drawing,

The operation of the above described relay of FIG; 1 Will now be explained in conjunction with the circuit diagram of FIG. 3. When switch S is closed and voltage is applied across the terminals 6 and 8, current will flow through the buckling member 10 and contacts 19 and 18 to energize the heater 30. A substantial current will also flow through the contacts 20 and 21 and coil 22 due to the initial low resistance of the coil. The remaining current will flow through the pull means 16 and junction 28 to resistor 24 and terminal 8. Since the coil 22 is in parallel With the pull means, there will be insuiiicient current in the pull means to expand it and operate the relay, As the coil is of the type having a positive temperature coecient of resistance, its resistance will increase during heating by heater 30 causing the current in the pull means to correspondingly increase. At a predetermined temperature of coil Z2, the current in the pull means is sufficient to expand it fully and thereby permit the buckling member to snap towards its normally biased position. Contacts 19 and 20 are thereby separated from their associated contacts and the circuit to the load terminal 4 is closed through the contacts 31 and 32. The time delay which is introduced into the relay corresponds to the heating time of the coil 22. With proper choice of coil and heater of the present invention, time delays of more than minutes can be realized. The coil for example can be an alloy of the type containing 99.8% nickel and having a wire diameter of .015 inch and a resistance at room temperature of 1 to 3 ohms. The heater resistance can be from 25 to 30 ohms while the pull means resistance can range from .2 to .6 ohm.

Opening of contacts 18 and 19, and 20 and 21 will not cool the pull means while the voltage is still present because current continues to flow through the pull means 16, fixed connection 28 and resistor 24 to negative terminal 8. The relay thereby energizes the load 36 until voltage is removed from the terminals. Since the heater 30 and coil 22 are cooling when the load is being energized, the relay is instantly reset when the voltage is removed.

Another embodiment of the invention will now be explained with reference to FIGS. 2 and 4 of the drawings.

The FIG. 2 embodiment is also a series type snap action device comprised of buckling member and pull means 16. As in FIG, 1, the support 12 for the buckling member is connected to the positive terminal 6 through Which the relay is energized. Terminal 8 is connected to the negative side of the source. In FIG. 4, an additional load 38 is shown as connected between a terminal 9 of the relay and the negative terminal of the source. Terminal 9 is connected to a support post 40 on the end of which is mounted a contact 42 positioned for engagement with a -contact 44 secured to the mid-point of the pull means. Contacts 42 and 44 are normally closed. A separate heater winding 46 surrounds a portion of pull means 16 and one end of the winding is connected to contact 4 32 while the other end is joined to a post 26 which is an extension of the negative terminal 8.

The operation of the relay of FIGS. '2 and 4 is as follows:

When the switch S is closed, the current through the pull means 16 is insuiiicient to expand it due to the parallel path through coil 22. The load 38 will be energized by the current through the parallel paths and heater 30 will also be energized through contacts 42 and 44. After a period of delay, during which time the heater 30 has increased the temperature of the coil 22, the current in pull means 16 becomes sucient to expand it so that the buckling member 10 snaps and assumes its normally biased position. In that position of the buckling member, the load 38 is deenergized due to the opening of normally closed contacts 42 and 44. Heater 30 is also deenergized and begins to cool. The load 36 is now energized through contacts 31 and 32 along with separate heater 46. As long as voltage is applied across the terminals of the relay, the separate heater 46 will maintain the pull means 16 in its expanded state. Upon removal of the voltage, the relay immediately resets.

The novel relay of the present invention has many applications where extended time delays are required before energization of the load. As an example, the relay of FIG. 3 can be adapted to operate as a device for Warning the drivers of automobiles or trucks that they are riding the brakes. By gauging the switch S with the brake pedal of the automobile, an effective warning device is obtained. The current from the automobile battery is applied across the relay when the switch S is closed by pressure on the brake pedal. The operation of the relay is then delayed for several minutes. Under normal braking conditions the load 36, which in this case may be a warning light on the dash board, will not be energized during the delay. If however, a driver inadvertently maintains pressure on the brake pedal for longer than the delay period, the relay operates and energizes the warning lamp which is placed in the line of vision of the driver.

The present invention is not limited to automotive uses but can also be utilized in other applications where time delays are required. Other examples are overload protection, starting motors, climate controls for air conditioners and recycling heaters.

The invention has now been described with reference to two embodiments thereof in each of which time delays of ve minutes or more can be obtained. The constructional features of the relay, for example, the shape of the vane, the orientation of the pull ribbon with reference to the deformation or the type of deformation therein could be varied within the scope of the invention so long as the relay itself is a series type snap action device. Although in FIG. 4 the heater winding has been shown as encircling less than half of the pull ribbon, more or less of the pull ribbon could be in heat conductive relaition with the winding and the winding need not encircle the pull ribbon as it could be placed in close proximity thereto to be in heat conductive relation therewith. Other ,modifications within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. A time delay relay comprising:

(a) an electrically conductive member adapted to move between a first position and a second position;

(b) an external load energized by said member in one of said positions;

(c) electrically conductive pull means that expand a predetermined amount upon the passage of electric current therethrough to move said member from said rst position into the said second position and back again upon contraction of said pull means which normally hold said member in said rst position;

(d) a source of electric current;

(e) a circuit for conducting said electric current through said pull means;

(f) a resistor having a positive temperature coeicient of resistance through which electric current flows in said circuit when said load is deenergized;

(g) said resistor being connected in said circuit in parallel with said pull means to reduce the flow of electric current supplied to said pull means and prevent the pull means from expanding said predetermined amount to move the member into said second position;

(h) an electric heater associated with said resistor;

and

(i) means for supplying electric current to said heater when electric current fiows in said circuit to heat the resistor and increase its resistance and increase the flow of electric current though said pull means to cause the pull means to expand said predetermined amount and move said member into said second position.

2. A time delay relay specified in claim 1 in which there is a fixed connection between the pull means and the circuit for conducting electric current through said pull means, the said circuit being adapted to continue the flow of electric current through said pull means when `the member is in the said second position to hold the pull means in its expanded state by the passage of current therethrough.

3. A time delay relay as specified in claim 1 wherein said conductive member is included within said circuit and further comprising a first and second contact positioned on the conductive member in a spaced relationship, two fixed contacts electrically connected to said resistor and said heater, said two fixed contacts being set for engagement with said first and second contacts when said conductive member is in said first position to thereby connect said resistor and heater across the pull means to determine the current through the pull means.

4. A time delay relay 4as specified in claim 3 wherein said first and second contacts are disengaged from said fixed contacts when the conductive member is moved into said second position to deenergize the resistor and heater so that the relay immediately resets upon removal of the source of electric current.

5. A time delay relay as specified in claim 1 wherein the pull means is electrically disconnected from said circuit when said conductive member is in the second position and further comprising a second electric heater associated with said pull means to heat the pull means when said conductive member is in said second position to maintain said conductive member in said second position.

6. A time delay relay as specified in claim S wherein said pull means carries a contact, said contact being set for engagement with a fixed contact connected to said circuit when said conductive member is in said first position and for disengagement when said conductive member in said second position.

k7. A time delay relay as specified in claim 6 wherein :an additional load is connected to said circuit for energization when said conductive member is in the first position.

8. A time delay relay as specified in claim 3 further comprising a third contact positioned on said conductive member adapted to engagement with an additional fixed contact connected to said external load when said conductive member is in said second position to energize said external load.

9. A time delay relay as specified in claim 1 wherein the external load is a warning signal light positioned on the interior of a motor vehicle to warn the driver of an unsafe condition.

10. A time delay relay as specified in claim 1 wherein said resistor is a nickel alloy coil with a high positive temperature coefficient of resistance.

References Cited UNITED STATES PATENTS 2,719,893 10/1955 Brady 337-137 2,756,305 7/1956 Broerman 337-113 2,945,933 7/1960 Di Girolamo et al. 337-113 JOHN W. CALDWELL, Primary Examiner HOWARD COHEN, Assistant Examiner U.S. Cl. X.R. 

